Generally, alumina, silica, carbon or other hard particles as residue in fluid catalytic cracking (FCC) for petroleum refinery are mixed in bunker C or other liquid as a main fuel for a marine diesel engine.
Excessive inflow of such particles into the engine, especially into a piston ring, a cylinder liner and the like of the engine, may cause adverse effects such as degraded sliding, seizing-up and mechanical wear. Thus, every time fuel is replenished, a ship management company samples and chemically analyzes the fuel to quantitatively grasp the particles in the fuel. When fuel with particles of not less than a stipulated concentration is replenished to a ship, the fact is notified of to the ship's crew to call their attention.
Conventionally, when particles in fuel are to be detected, sampled fuel is filtered through a filter or the like and a residue is microscopically observed or quantitatively analyzed to detect particles.
State-of-the-art technology with respect to a method for detecting a concentration of particles and a device therefor is shown, for example, in Patent Literature 1.